1. Field of the Invention
This invention relates to semiconducting devices, and more particularly to a memory device including a phase change material that has electrical properties of a field effect transistor and/or bipolar transistor.
2. Background of the Invention
Phase change materials may exhibit at least two different states, which may be amorphous or crystalline. The amorphous state involves a more disordered crystal structure.
Transitions between these states may be selectively initiated. The phase change may be induced reversibly. Of particular interest are chalcogenide alloys, which contain one or more elements from Group VI of the Periodic Table of Elements.
Phase change materials are used in standard bulk silicon technologies to form the memory elements of nonvolatile memory devices. Each memory cell may be thought of as a variable resistor, which reversibly changes between higher and lower resistivity states corresponding with the crystalline state of the phase change material. The states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. The phase change material allows for the storage of data because each phase of the phase change material may be distinguished by its' resistance.
In these devices, the phase changes of the memory element in the memory devices are accomplished by direct heating of the phase change material with high programming currents. Conventionally, bipolar transistors are used to deliver high programming currents by directly heating the phase change material. Due to the high current, direct heating of the phase change material can cause the phase change material to degrade over repeated programming operations, therefore reducing memory device performance.
A phase change memory device is needed that overcomes memory device degradation due to direct heating of the phase change material. Moreover, a phase change memory device is needed that further reduces the minimum memory cell area of a memory array layout.